In the past, a reading apparatus such as a scanner or an image forming apparatus such as a printer, a copying machine, or a multi-function peripheral (MFP) reads an image of an original document by focusing the image of the original document on an image sensor using a light-emitting device such as an LED and a lens array in which a plurality of lenses are arrayed. Further, the apparatus focuses, using the light emitting device such as the LED and the lens array, a ray from the LED on a photoconductive drum via the lens array and forms (exposes) an image on the photoconductive drum. As the lens array, there is a lens array in which a plurality of lenses and apertures are combined.
In a lens array arranged one-dimensionally, the depth of focus and the depth of field in a sub-scanning direction are large compared with those in a main scanning direction. If an object plane or an image plane deviates from a design value, blurring conditions are different in the main scanning direction and the sub-scanning direction. This causes a sense of discomfort for a user who looks at a scan image in a CIS including the lens array and an output image in an LED scanning head.
A technique is disclosed for improving MFT and a light amount and suppressing fluctuation due to a place and the like by, in a lens array in which lens surfaces are arranged in a row in the main scanning direction, setting the diameter of the lens surfaces in the sub-scanning direction larger than a pitch among lens elements in the main scanning direction. However, this technique does not take into account the balance of characteristics (resolution) that should be kept if the object plane or the image plane deviates from the design value. Therefore, the same problem occurs in the scan image in the CIS including the lens array and the output image in the LED scanning head.